1. Field of the Invention
The present invention relates to oscillators and in particular magnet-based oscillators that are low duty cycle.
2. Description of the Art
Magnetostrictive transducers having elongated waveguides that carry torsional strain waves induced in the waveguide when current pulses are applied along the waveguide through a magnetic field are well known in the art. A typical linear distance measuring device using a movable magnet that interacts with the waveguide when current pulses are provided along the waveguide is shown in U.S. Pat. No. 3,898,555.
Devices of the prior art of the sort shown in U.S. Pat. No. 3,898,555 also have the sensor element in a housing which also houses the electronics to at least generate the pulse and receive the return signal. The amplitude of the return signal detected from the acoustical strain pulse is, as well known in the art, affected by many parameters. These parameters include the position magnet strength, waveguide quality, temperature, waveguide interrogation current, and assembly tolerances.
A low duly cycle oscillator is used to provide a relatively short pulse width at a relatively long period repitition rate. An example would be the waveguide driving circuit for a magnetostrictive position sensor. This type of driving circuit of the prior art supplies a one or two microsecond pulse at a repetition rate with a period of one millisecond to one second. A one microsecond pulse with a repetition rate having a period of one millisecond would be a duty cycle of only 0.1% this function is usually accomplished by driving a one microsecond monostable multivibrator from the output of a one kilohertz oscillator. A similar function is usually required in ultrasonic sensors or other time-of-flight measurement circuits.
Several types of magnetic-based sensors are available for measuring linear or rotary position. Magnetic-based sensors have an advantage in that they provide non-contact sensing; so there are no parts to wear out. Examples of magnetic-based sensors are LVDTs, inductive sleeve sensors, and magnetostrictive sensors.
A first previous version of low duty cycle oscillators used in, for example, magnetostrictive devices, have used a combination of a 50% duty cycle low frequency oscillator and a monostable multivibrator (one-shot) as shown in FIG. 1. The oscillator sets the repetition rate and the one-shot outputs the short duration pulse.
A second previous version of a low duty cycle oscillator has been based on a standard oscillator using one or more digital gates, where the charge up and charge down times are steered through different paths by using one or more diodes, as shown in FIGS. 2 and 3. This circuit can satisfy some requirements, but has a substantial temperature coefficient because of the approximately 2.2 mV per degree celcius temperature coefficient of the diode forward voltage drop. The forward voltage drop of approximately 0.6V is also an error that must be accounted for in the timing and performance characteristic calculations.
A third previous version of a low duty cycle oscillator has used software control of a microcontroller output port to produce the desired dutycycle. This is inexpensive, but requires a high degree of dedication of the microcontroller capability to performing this simple function.
It is an object of the present invention to employ a simple circuit to accomplish producing a relatively short pulse at a relatively long period repetition rate.
The present invention relates to a simple circuit to realize the function of a low duty cycle oscillator (less than 50% and preferably 10% or less) to provide a relatively short pulse width at a relatively long period repetition rate by using common integrated circuit components. The I.C. components comprise several copies of the same function in one package. Portions of these multi-part components, sufficient to implement the instant circuit, are often left unused in a typical circuit design application. Therefore, this circuit can be implemented with little additional expense and overcomes the inefficiency and inaccuracies of the prior art.